Climate Science Glossary

Term Lookup

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Term:

Settings

Beginner Intermediate Advanced No DefinitionsDefinition Life:

All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

It amazes me how many "skeptics" simultaneously believe that the earth's climate wildly varied in the past, while also believing the earth is only 6000 years old. I would pay a million bucks for a report to ask Governor Perry about this apparent contradition of his anti-scientific views.

since climate has changed in the past we can't be sure that it isn't natural now...

followed by
since Obama didn't get excited about it in the last state of the Union, and Gore doesn't live like the Amish the we can be sure it isn't really problem. We can judge this by how political leaders walk the walk, rather than taking the trouble to examine the science ourselves.

A. Less than humans have emitted so far. Since the Industrial Revolution the Earth has warmed 0.8°C, but we are already committed to a further 0.6°C because of 'warming in the pipeline' - primarily the lagged response of ocean warming.

In fact some land areas of the Earth are already committed to extreme warm temperatures because of the CO2 humans have released through fossil fuel burning. (coincidentally I'm writing up a blog post on this very point)

Moderator Response: [Dikran Marsupial] A one year time frame is not very sensible in a discussion of climate. The thermal inertia of the oceans means that a very large change in forcing would be required for an immediate (one year) change of global temperatures of one degree, which would result in a truly catastrophic change in equilibrium temperature once all the warming had been realised. As a result I doubt anyone has performed a model run or calculation that gives a direct answer to the question. I'd be mildy interested in the answer though if anyone has.

One year is almost a no-feedback scenario, barely enough time to get water vapour operating. On that basis, I guess, with 0.3 per doubling, then you would need 3 doublings for 1 degree rise. Of course, 10 years after that...
Timeframe matters because of both thermal inertia and lag in feedback response which have time range from few years to hundreds of years. (eg the albedo feedback from melting ice is limited by physics of melting).

If there is a direct relationship to CO2 and temperature this syllogism would be valid. If this can be falsified, then the syllogism will not hold, or the correlation between CO2 and temperature MAY not be a truth value.

00

Moderator Response: [Dikran Marsupial] The direct effect of CO2 radiative forcing on equilibrium temperatures is about 1 degree C per doubling. This is not contested, even by skeptic scientists such as Pat Michaels and Roy Spencer. This there is a direct relationship between CO2 and temperature and it is directly falsifiable. Thus the syllogism is valid. Poppers' theory of falsification does not require that the falsification should be possible within a particular timescale, so equilibrium sensitivity is perfectly adequate for "scientific acceptability"; please lets not have yet another thread devolve into pointless irrelevant epistemological discussions.

Moderator Response: [Dikran Marsupial] No, of course not, however climatology is based on physics, if someone wants to claim that negative feedback will prevent CO2 from causing warming then (i) they need to provide physics that support negative feedback of that magnitude (ii) be able to explain events from paleoclimate that pretty much rule out that degree of negative feedback.
No more discussion of epistemology on this thread; it is unnecessary for a discussion of the science at the level appropriate for a forum of this nature. You need to understand the science before epistemological issues are worth discussing.

Ok, I will try and stay away from any epistemological statements. I am curious though and from what I can gather, you are saying that the physics of a GHG MUST always result in warming, but there could be counter scenarios that will itself counteract the resulting warming.

Am I on point?

00

Moderator Response: [Dikran Marsupial] It is unhelpful to discuss scientific issues in absolute terms (e.g. MUST, certain, always) as if someone is being ultra-pedantic it introduces the opportunity for evasion of the substantive topics via quibbling. Thus I wouldn't say that GHG MUST always result in warming, but I would say that there is no credible evidence or physical theory to suggest that GHGs wont always result in warming. This is mostly because the theories that suggest strong negative feedback and hence low climate sensitivity are generally unable to explain paleoclimatic events (unlike theories that suggest climate sensitivities considered plausible by mainstream scientific opinion).

Dana69 - I'll have to ask you to excuse my interpretation, but you appear to be hunting for reasons to deny CO2 warming. While the epistemology of math is an interesting subject in itself, epistemology is quite a different realm from the accumulated physical evidence, and I must view your introduction of it as a red herring.

The direct effect of doubling CO2 is ~1°C warming. Feedbacks look to amplify that to a climate sensitivity of ~3°C. There is essentially zero evidence for sufficient negative feedback to suppress that forcing. Please read that link for a discussion of the evidence in this regard.

Yes, Dana, given the current Earth system and the likelihood of its persistence, GHGs must result in warming. Other things might overwhelm that warming, but GHGs will STILL be acting to warm. It's all about the net effect of all forcings and feedbacks.

"From the available evidence it is quite clear that human emissions are the main cause of the increase of CO2 in the atmosphere. There is a small influence of temperature on this increase, as warmer oceans emit some CO2 (but warmer land absorbs more CO2 in vegetation!). But the influence of temperature is limited: based on the variability of the CO2 increase around the trend, the short-term (1-6 months) ratio is about 3 ppmv/ºC (based on the 1992 Pinatubo and 1998 El Niño events). The very long term influence of temperature on CO2 levels (Vostok ice core) is about 8 ppmv/ºC. Thus at maximum, the influence of temperature on the current increase is 0.7 ºC x 8 ppmv/ºC = 5.6 ppmv of the about 100 ppmv increase since the start of the industrial revolution.

There are only two fast main sources of CO2 to the atmosphere, besides the burning of fossil fuels: oceans and vegetation. Vegetation is not a source of CO2, as the oxygen deficiency (in 5.5) showed. Neither are the oceans, as the 13C trend (in 5.3) and the pCO2/pH (in 5.6) shows. This is more than sufficient to be sure that human emissions are the cause of most of the increase of CO2 in the atmosphere of the past 1.5 century.

Thus we may conclude:

All observed evidence from measurements all over the earth show with overwhelming evidence that humans are causing the bulk of the increase of CO2 into the atmosphere.

But...

That humans are the cause of the recent increase of CO2 doesn't tell anything about the influence of increased CO2 on temperature!

Humans may be responsible for (a part of) the temperature increase. How much, that is an entirely different question, as that mainly depends of the (positive and negative) feedbacks that follows any increase of temperature..."

Seems like everything is contained in here and gives credit to both sides. No denying, same physics, yet diverse conclusions.

00

Moderator Response: [Dikran Marsupial] Please do us a favour and go and read the technical summary to the IPCC WG1 report. You will find there that not all of the observed warming is attributed to AGW, so you are arguing against a position that nobody is actually taking.
Your statement that "That humans are the cause of the recent increase of CO2 doesn't tell anything about the influence of increased CO2 on temperature!" is also a non-sequitur. The influence of CO2 on temperatures is established by physics (theory, experiment and observation), and remains true whether we are emitting CO2 or not.
BTW, the observed rise is 100% anthropogenic. I'll happily discuss how we know that to be true on a more appropriate thread.

I am not sure why it repeats, I am truly not trying to do that. Please forgive me.

00

Moderator Response: [Dikran Marsupial] No problem, it has happened before. It is probably becuase you are using the reload button, or the forward and backward buttons to navigate, which in some circumstances can resend the post.

Dana, do you accept that humans are the source of the recent and rapid rise of atmospheric CO2? And do you accept that increased CO2 is always a positive forcing on temp (whatever else is going on)?

It's important that we establish something, or else we end up like middle-class sophomore philosophy majors: all talk and no performance--all theory and no practice. No one has the patience for that here.

Most of the discussion on this site is now in the realm of determining the influence of various forcings and feedbacks beyond GHGs. The science reflected in the IPCC-supported sensitivity models is robust, and there are hundreds of links on this site that you can follow to get a feel for that robustness. Note that there is no "other side." There is no comprehensive alternative theory widely supported by some "other side." If you tried to create a physically consistent model out of all of the attacks on the theory of AGW, you'd fail miserably. That's why SkS isn't set up on an "us vs. them" either-or framework.

If you want to understand sensitivity, there are plenty of other articles and threads on SkS where you can do this (with semi-live people willing to take part).

Just a note on Dikran's moderator comment to #17... I presume that the second to last sentence, "BTW, the observed rise is 100% anthropogenic", is referring to the rise in CO2 rather than the rise in temperature. I make this assumption because otherwise Dikran would be incorrect, and that just can't be the case. :]

00

Moderator Response: [Dikran Marsupial] Yes, absolutely correct. The rise in CO2 is 100% anthropogenic, the rise in temperatures is not.

Let me answer your question first then ask a follow up question that has bugged me.

1) Yes I agree that humans are the source of the most recent and rapid rise of CO2 in the troposphere (not sure if the distinction is relevant)

2) Yes, I do accept that CO2 is a positive forcing on temperature.

Now my main point of incongruity is from this site itself.

Note: "When the Earth comes out of an ice age, the warming is not initiated by CO2 but by changes in the Earth's orbit. The warming causes the oceans to give up CO2. The CO2 amplifies the warming and mixes through the atmosphere, spreading warming throughout the planet. So CO2 causes warming AND rising temperature causes CO2 rise."

I am ok with this, but what I cannot wrap my tweener brain around is how to explain the opposite affect. Meaning, there must be a point where temperature reverses and starts to decline, but CO2 levels MUST be higher, YET do not affect this reversing trend of the earth falling back into an ice age. Unless the new hypothesis states that since man is contributing all this additional CO2 there will be no new ice age, and that man has permanently altered this process through the increase in man-made CO2 levels.

No matter what you label me, this is something that sticks out in my head. If this is true, there seems to circumstances which appear to counteract the conclusion that CO2 is ALWAYS a forcing.

Also, I read GMB post#10 at 16:57 PM on 27 December, 2007 under CO2 lags Temperature. It was a much different take on the subject, but I notice no one answered when he states:

"This idea that Malinkovitch needs CO2 feedback to do the job is clearly false. Since it relies on a WATTS-PER-SQUARE-METRE model which is a light-and-air-only model.

"If we allow for the accumulation and decumulation of joules in the planet and the oceans then it is the factor of TIME ALONE that needs to be taken into account and not this sideshow of CO2-feedback.

We ought to be looking at a model which relies on STRATA AND HEAT BUDGETS."

I pray that I have made myself clear, because I hate all these denier labels and I know you feel these might be sophomoric questions.

Thanks in advance, and oh by the way, I have read the IPCC reports, and for one in search of knowledge they are no help.

00

Moderator Response: [Dikran Marsupial] you write "No matter what you label me", please can you avoid this sort of thing, SkS works best when everybody concerned keeps everything on a calm impersonal scientific basis. This sort of statement comes across badly (it implies that the other parties in the dicussion are looking to label you, which is unfair to them).
Now if the IPCC reports are not much help, that probably means you need to start with something a little more basic (e.g. Houghton's book).
Lastly, if there is something you don't understand, or you want to ask a question, it is best simply to ask a direct question without the extensive quoting or digressions.

Dana: "I am ok with this, but what I cannot wrap my tweener brain around is how to explain the opposite affect. Meaning, there must be a point where temperature reverses and starts to decline, but CO2 levels MUST be higher, YET do not affect this reversing trend of the earth falling back into an ice age. Unless the new hypothesis states that since man is contributing all this additional CO2 there will be no new ice age, and that man has permanently altered this process through the increase in man-made CO2 levels."

Why do you have a problem with orbital forcing driven CO2 increases stopping when the orbital forcing does? That would seem self-evident... yet in #21 you appear to hold it out as some sort of 'obvious flaw'. I can't figure out what you think is 'wrong' with it.

If you look at the ice core CO2 records of past glaciation cycles you will see that CO2 'quickly' (~10,000 years) rises from ~180 ppm to ~280 ppm and then slowly drifts back down. Looking more closely at the current cycle CO2 levels had been at 280 ppm +/- 10 for a few thousand years prior to the industrial revolution. In short, CO2 levels had not changed significantly for a long time and thus were not causing any additional warming of the planet. As the orbital forcing reverses we would then see cooling from that... which would result in a decreasing atmospheric CO2 feedback and thus more cooling.

Obviously the 'recent' large human CO2 emissions have changed this, but the point is that CO2 levels from natural emissions had leveled off... and perforce warming from them had done so as well. There wasn't any 'ongoing warming' to prevent cooling from the orbital shift. CO2 feedback effects do not self perpetuate ad infinitum... otherwise the planet would have burned to a crisp long ago.

"I am curious though and from what I can gather, you are saying that the physics of a GHG MUST always result in warming, but there could be counter scenarios that will itself counteract the resulting warming."

Well the obvious one is where the increase in GHG is also accompanied by an increase in aerosols with a similar magnitude of forcing. However, aerosols are shortlived in the atmosphere compared to CO2, so if the GHG is CO2, then warming results as aerosol declines.

As to what happens in the ice reversal, well see the appropriate thread, but when solar declines in NH, albedo increases, cooling starts, and the feedback mechanisms for GHG (methane sources freeze and then as ocean cools, CO2 is absorbed, etc) work in reverse to amplify cooling.

00

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.